This study reports a new nonfullerene electron transporting material (ETM) based on naphthalene diimide (NDI) small molecules for use in high-performance perovskite solar cells (PSCs). These solar cells simultaneously achieve high power conversion efficiency (PCE) of over 20% and long-term stability. New NDI-ID (N,N′-Bis(1-indanyl)naphthalene-1,4,5,8-tetracarboxylic diimide) consisting of an N-substituted indane group having simultaneous alicyclic and aromatic characteristics is synthesized by a low-cost, one-step reaction, and facile purification method. The partially flexible characteristics of an alicyclic cyclopentene group on indane groups open the possibility of lowtemperature solution processing. The conformational rigidity and aromaticity of phenyl and alicyclic groups contribute to high temporal stability by strong secondary bonds. NDI-ID has herringbone packed semiconducting NDI cores that exhibit up to 0.2 cm 2 V −1 s −1 electron mobility in field effect transistors. The inverted PSCs based on CH(NH 2 ) 2 PbI 3-x Br x with NDI-ID ETM exhibit very high PCEs of up to 20.2%, which is better than that of widely used PCBM (phenyl-C61-butyric acid methyl ester) ETM-based PSCs. Moreover, NDI-IDbased PSCs exhibit very high long-term temporal stability, retaining 90% of the initial PCE after 500 h at 100 °C with 1 sun illumination without encapsulation. Therefore, NDI-ID is a promising ETM for highly efficient, stable PSCs.

In organic hole-transporting material (HTM)-based p−i−n planar perovskite solar cells, which have simple and low-temperature processibility feasible to flexible devices, the incident light has to pass through the HTM before reaching the perovskite layer. Therefore, photo-excited state of organic HTM could become important during the solar cell operation, but this feature has not usually been considered for the HTM design. Here, we prove that enhancing their property at their photo-excited states, especially their transition dipole moments, can be a methodology to develop high efficiency p−i−n perovskite solar cells. The organic HTMs are designed to have high transition dipole moments at the excited states and simultaneously to preserve those property during the solar cell operation by their extended lifetimes through the excited-state intramolecular proton transfer process, consequently reducing the charge recombination and improving extraction properties of devices. Their UV-filtering ability is also beneficial to enhance the photostability of devices.

A design strategy is proposed for electron‐transporting materials (ETMs) with homochiral asymmetric‐shaped groups for highly efficient non‐fullerene perovskite solar cells (PSCs). The electron transporting N,N′‐bis[(R)‐1‐phenylethyl]naphthalene‐1,4,5,8‐tetracarboxylic diimide (NDI‐PhE) consists of two asymmetric‐shaped chiral (R)‐1‐phenylethyl (PhE) groups that act as solubilizing groups by reducing molecular symmetry and increasing the free volume. NDI‐PhE exhibits excellent film‐forming ability with high solubility in various organic solvents [about two times higher solubility than the widely used fullerene‐based phenyl‐C61‐butyric acid methyl ester (PCBM) in o‐dichlorobenzene]. NDI‐PhE ETM‐based inverted PSCs exhibit very high power conversion efficiencies (PCE) of up to 20.5 % with an average PCE of 18.74±0.95 %, which are higher than those of PCBM ETM‐based PSCs. The high PCE of NDI‐PhE ETM‐based PSCs may be attributed to good film‐forming abilities and to three‐dimensional isotropic electron transporting capabilities. Therefore, introducing homochiral asymmetric‐shaped groups onto charge‐transporting materials is a good strategy for achieving high device performance.

Intercorrelation of thermoelectric properties of a doped conjugated semiconducting polymer (PIDF-BT) with charge carrier density, conductive morphology, and crystallinity are systematically investigated. Upon being doped with F4-TCNQ by the sequential doping method, PIDF-BT exhibited a high electrical conductivity over 210 S cm–1. The significant enhancement of electrical conductivity resulted from a high charge carrier density, which is attributed to the effective charge–transfer-based integer doping between PIDF-BT and dopant molecules. Based on the systemic characterization on the optical, electrical, and structural properties of doped PIDF-BT annealed at different temperatures, we investigated the characteristic correlations between thermoelectric properties of PIDF-BT films and their four-probe electrical conductivity, charge carrier density, and charge carrier mobility obtained from AC Hall effect measurements. This study revealed that exercising fine control over the crystallinity and conductive migration of the conjugated polymer films can be a strategic approach to suppressing the degradation of the Seebeck coefficient at high charge carrier density and ultimately to maximizing the power factors of organic thermoelectric devices.

No abstract